Is this boiler safe?

[Parky]

The flue of my neighbour's gas boiler discharges on the access way between our houses, and it "pops" when it ignites, i.e. a mini-explosion, (which makes me jump if it happens when I walk past). He has consulted British Gas, who say it's not a problem and they will come and have a look after Covid restrictions are lifted. All the boilers I have ever seen ignite quietly, so is this "popping" safe?

[tacpot12]

It sounds like the spark is not optimal - the boiler isn't lighting the moment that there is sufficient gas available for combustion, but it is unlikely to be dangerous. All boilers have a way to sense if the gas that is being admitted is being burnt or not, and should cut off the gas supply before any significant build up of unburnt gas inside the boiler occurs.

[Mike4]

The flue of my neighbour's gas boiler discharges on the access way between our houses, and it "pops" when it ignites, i.e. a mini-explosion, (which makes me jump if it happens when I walk past). He has consulted British Gas, who say it's not a problem and they will come and have a look after Covid restrictions are lifted. All the boilers I have ever seen ignite quietly, so is this "popping" safe?

The term for this is "explosive ignition", and no, it is not regarded within the industry as safe. It needs dealing with.

Having said that, explosive ignition usually results in 18" of flame flashing out of the flue terminal, and your description of 'popping' sounds rather trivial in comparison. The main risk is to the user of the boiler though, where explosive ignition is extreme cases will blow the front off the boiler.

Bottom line is, I don't actually know what happens about a privately owned boiler presenting a risk to the general public. My advice would be to call Gas Safe register and tell them the boiler next door has explosive ignition and you're worried about it. They run a help line for the public with questions like this. Well they used to. I just checked their website and they unhelpfully no longer list a number for you to ring. You could try ringing the technical helpline for us gas bods, 0800 408 5577. Don't tell'em where you got the number!

A better idea might be to call the gas emergency number 0800 111999 and insist you can smell gas from the flue terminal before it goes pop. Saying you can smell gas presses all manner of buttons.